This invention relates to an in-tank type electric fuel pump which is built in the fuel tank of a motor vehicle or the like to supply fuel to the engine under pressure, and more particularly to an improvement of the fuel discharge efficiency of the electric fuel pump.
FIG. 4 is a side view, with parts cut away, showing the arrangement of a conventional electric fuel pump of this type. FIG. 5 is a sectional view taken along V--V in FIG. 4.
In those figures, reference numeral 1 designates a disk-shaped impeller having vane grooves 1a formed in its peripheral portion in such a manner that they are extended radially; 2, a pump cover with a slide surface 2a which confronts with one surface of the impeller 1 with a small gap therebetween, thus supporting the impeller 1; 3, a pump base having a slide surface 3a which confronts with the other surface of the impeller 1 with a small gap therebetween, thus supporting the impeller 1; 4, an arcuate-belt-shaped pump chamber provided outside the slide surfaces 2a and 3a of the pump cover 2 and the pump base 3 and along the periphery of the impeller 1; 5, a fuel suction inlet provided on the side of the pump cover 2; and 6, a pump chamber outlet provided on the side of the pump base. Those components 2 through 6 form a pump casing 7. Further in FIGS. 4 and 5, reference numeral 8 designates a motor shaft on which the impeller 1 is mounted; 9, an armature; 10, magnets; 11, a cylindrical housing on which the magnets 10 is mounted, the housing 11 being engaged with the pump casing 7. Those components 8 through 11 form a motor section 12. Further in FIGS. 4 and 5, reference numeral 13 designates the motor chamber of the motor section 12; and 14, a fuel discharge outlet.
When the motor section 12 operates, the impeller 1 is rotated, so that a fuel (not shown) is sucked through the fuel suction inlet 5 into the fuel pump body. The fuel thus sucked is pressurized in the pump chamber 4, so that it is supplied through the pump chamber outlet 6 into the motor chamber 13, and then discharged through the fuel discharge outlet 14.
In the above-described regeneration type electric fuel pump, in order to prevent the lowering of its discharge efficiency; i.e., a loss of fuel leakage which occurs between the surfaces of the impeller and the slide surfaces of the pump cover and the pump base, the gaps in the direction of thrust are held minimum at all times. Hence, when the pressure of the fuel in the pump chamber is increased from the fuel suction inlet towards the pump chamber outlet by rotation of the vane grooves, in the pump casing the pressure near the pump chamber outlet is unbalanced with that near the fuel suction inlet, so that the impeller is rotated while contacting the part of the pump casing which confronts with the pump chamber outlet. FIG. 5 shows scratches 15 which are formed on the pump casing when the impeller contacts the pump casing near the pump chamber outlet. As a result, the rotation of the impeller 1 is subject to increased frictional resistance, and therefore the motor is decreased in the speed of rotation, and power consumption is increased. That is, the electric fuel pump is subject to decreased discharge efficiency.